The popularity of indoor flying toys, particularly ultra-light slow flying airplanes and self-propelled lighter-than-air flying toys (LTAs) (e.g., miniature balloons or blimps), is increasing. Indoor airplanes, such as shown in FIGS. 1(a)-1(c) comprise a single wing 50 and tail structure 55 are disposed on a frame 60. A drive system including a propeller 10, a motor 15 and associated power source 20 (e.g., a battery or other charge storing device) or other power providing device (e.g., a rubber band, compressed gas) is provided to impart rotation to the propeller via a drive shaft. Indoor airplanes electric motors are conventionally powered by lithium-ion or nickel-metal-hydride (NiMH) batteries and, more recently, lithium-polymer (LiPo) batteries. A receiver 25 may be optionally provided in combination with a speed control device and/or actuating device(s) 30 (e.g., electromagnetic coils) to permit actuation of controls or control surfaces (e.g., the rudder or stabilizer) to change flight characteristics during flight. Power systems and controls (e.g., a 3-channel control for rudder, throttle, and elevator) may also combined with indoor LTAs.
Indoor flight of such airplanes and lighter-than-air flying toys broadly includes any enclosed area such as an armory, auditorium, school gymnasiums, convention centers, or the like. Historically, given the speed and size of the indoor aircraft, large spaces were required to accommodate the flight characteristics of the indoor aircraft. For example, indoor micro-RC (radio controlled) or scale-RC model airplanes having specified minimum wing areas (e.g., greater than 135 in.2), power plants (e.g., GWS IPS DXA 5.86-1 motor/gear unit), propellers, batteries (e.g., 2 lithium-poly cells or 6 nickel-cadmium or nickel-metal-hydride cells), and weights (e.g., between about 7-8 ounces) are typically flown in relatively large indoor areas (e.g., school gymnasiums) in pylon racing competitions sponsored by NIRAC (National Indoor Remote Control Aeromodeling Council). The specifications for a particular competition may vary. NIRAC also sponsors indoor RC scale events wherein models are powered by electric, CO2, compressed air, or rubber bands, the models cannot weigh more than 12 ounces, and the models must have a maximum wing loading not to exceed 6 ounces per square foot.
Over time, advances in power plants and materials have permitted smaller and slower airplanes to fly within smaller and smaller areas, thus taking indoor flight out of the province of the professional modeler or skilled hobbyist and into the realm of the general public. Presently, slow flying airplanes are provided to fly within small enclosed areas (e.g., a 10′×10′ room), such as rooms within houses or living quarters. Conventional slow flying airplanes include the Ikara “Firefly” Indoor Airplane, a rubber-powered free-flight glider from Hobby-Lobby International Inc. of Brentwood, Tenn. USA. The “Firefly” has a wingspan of about 7″ and an RTF of about 2.7 grams (0.10 oz.) and is capable of flight in a circle of about 10′ diameter for 45 seconds to 2 minutes, depending on the configuration. A similar indoor plane, called the “Kolibri”, has a wingspan of 8.5″ and a weight of 3 grams. Other indoor ultra-light slow-fly models include the “Celine” sold as a kit by Didel of Belmont/Lausanne, Switzerland, and shown in FIGS. 1(a)-1(c). These ultra-light slow-fly models generally fly at speeds of between about 1.0-1.5 m/s and are constructed from conventional light-weight parts such as, but certainly not limited to, Didel 4 mm coreless motors, gear boxes, bird (built-in-rudder-device) actuators, and IR receivers.
Improvements to indoor planes typically focus on decreasing the overall weight of the aircraft to improve the power to weight ratio or lift to drag ratio and the flight time of the airplane. However, structural integrity of the plane or airship, particularly of the propeller and the propeller-to-frame connection, is often overlooked. Accordingly, a need exists for a lightweight structure for protecting the propeller(s) of indoor flying toys, such as but not limited to the aforementioned types of indoor flying toys.